This invention relates generally to organic light emitting device (OLED) displays that have light emitting layers.
Organic light emitting device (OLED) displays use layers of light emitting materials. Unlike liquid crystal devices, the OLED displays actually emit light that may make them advantageous for many applications.
Some OLED displays may use at least one semiconductive conjugated polymer sandwiched between a pair of contact layers. Other OLED displays may use so-called small molecule materials. The contact layers produce an electric field that injects charge carriers into the polymer layer. When the charge carriers combine in the polymer layer, the charge carriers decay and emit radiation in the visible range.
It is believed that polymer compounds containing vinyl groups tend to degrade over time and use due to oxidation of the vinyl groups, particularly in the presence of free electrons. Since driving the display with a current provides the free electrons in abundance, the lifetime of the display is a function of total output light. Newer compounds based on fluorine have similar degradation mechanisms that may be related to chemical purity, although the exact mechanism is not yet well known in the industry. In general, OLED displays, in general, have a lifetime limit related to the total output light. This lifetime is a function of intrinsic lifetime and the display usage model.
The gradual decrease in display output, at constant current, can be compensated by a corresponding increase in current. However, the degradation may not be uniform across the display. If some of the pixels of the display are degraded non-uniformly, a uniform increase in current does not solve the non-uniform degradation problem. Even after compensation, some pixels will be brighter than other pixels.
Thus, there is a need for better ways of controlling OLED displays.